Multiple myeloma remains a largely incurable disease with current therapy. Allogeneic BMT provides an opportunity to add the potential antitumor effect of marrow grafts to those of high dose chemoradiotherapy. One potential strategy for enhancing a graft vs. tumor effect without aggravating graft vs. host disease would be to selectively target an immune response against a defined tumor-specific antigen. The idiotype of the rearranged immunoglobulin gene product of a myeloma can serve as a unique tumor-specific antigen for vaccine development. We are testing the hypothesis that tumor antigen-specific immunity can be adoptively transferred to BMT recipients by active immunization of marrow transplant donors with purified myeloma idiotype protein, conjugated to a carrier protein (KLH) and administered with GM-CSF as an immunological adjuvant. The objective of this protocol is to induce cellular and humoral immunity in marrow transplant donors and recipients against the unique idiotype expressed by the recipients myeloma. Pts. under 60 with an HLA-matched sibling donor, and who are in a PR prior to allogeneic BMT, are eligible. HLA matched sibling donors receive a series of 3 vaccinations during an 8-wk. period prior to bone marrow harvest. Recipients concurrently receive vaccinations pre-BMT, as well as three booster vaccinations at wks. 12, 16, 24 post-BMT. IdKLH (0.5 mg) is administered s.c. GM-CSF (250 microgram/m2) is administered s.c. locally with the vaccine on the day of vaccination and for the 3 consecutive days following vaccination. 3 donor-recipient pairs have been enrolled on the study. 2 donors have been successfully immunized against their respective recipients myeloma idiotype, and the corresponding recipients have just recently completed BMT.